I feel like im losing top end in 4th gear,,,,
ive got a ford 9" - 3.89 gears
i think with the 3.89's with 350rwhp is too much
Do you think i could gain alot more back with some 3.73's
is it worth spending the money....

 

you gear so you're at peak hp when crossing the quarter mile.

 

what is your 1/8 mile speed vs 1/4?
that will tell you if you are running out of gear..
I doubt it though..
3.89's will put you through traps 119 mph at 6000 with a manual and probably a little more if using slicks due to growth of tire.
so 5500 will get you 109, I don't know your combo, but unless TPI
I doubt its out of steam at 5500.

As X said, its not really dependant on HP, rather effeciency.. You want to be slightly past peak HP through the traps.. That way you stay in your max power more often through 1/4. But in a street car, you will make trade-offs.
Maybe not be perfectly effecient and lose .1 to keep a friendlier gear.